Compressors in which an inverter motor is employed are common in scroll compressors used in outdoor units of air conditioners or the like in order to expand the range of performance; however, in order to obtain an even greater range of performance, operation at even higher levels of rotation is currently being demanded.
Nevertheless, an adverse effect of high-rotation operation is the increased likelihood that the spiral lap of the movable scroll or the like will be damaged.
Specifically, when high-rotation operation is performed, the centrifugal force of the orbiting movable scroll increases, and the centrifugal force of the movable scroll acts between a crankshaft constituting a drive shaft and a boss constituting a bearing portion of the movable scroll, or between the lap of the movable scroll and the lap of the fixed scroll.
The shape of the spiral laps may vary from the ideal in actual processing; in particular, since the winding end part on the outermost periphery of the lap of the moving scroll is in a state of being supported on one side, processing error readily arises, and contact is readily made with the lap of the fixed scroll.
If the winding end part on the outermost periphery of the lap of the fixed scroll is shaped as a thick, highly rigid block and not a thin blade, then when the laps of the movable scroll and the fixed scroll make contact, substantially no bending of the lap on the fixed scroll occurs; i.e., less stress-relief clearance is provided. The stresses visited on the corresponding lap of the movable scroll accordingly increase.
As described above, the centrifugal force applied to the movable scroll lap is increased by high-rotation operation, making it necessary for the lap to be shaped so as to be capable of withstanding the centrifugal force.
Examples of shapes widely known in the art for laps whose spiral shape is configured according to an involute curve include shapes where the wall thickness of the lap is fixed from the winding start part to the winding end part (i.e., the base radius of the involute is fixed), and/or shapes where the wall thickness of the lap decreases closer to the winding end part on the outermost periphery relative to the middle winding start part of the lap (i.e., the base radius of the involute decreases).
Therefore, in order to improve the strength of the winding end part of the lap in the scroll compressor taught in Japanese Examined Patent Application No. 5-29796, the wall thickness of the lap is fixed from the winding start part to the winding end part, but a protruding part is provided on the outside of the lap on the winding end part of the lap of the movable scroll.
Moreover, according to the scroll compressor taught in Japanese Unexamined Publication No. 2000-179478, the wall thickness of the lap is constant from the winding start part to the winding end part, but the winding end part of the lap of the movable scroll is extended, and the plate thickness is less than the other portions of the lap.